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In 2010, 6.7 percent of the human beings on Earth lived in a megacity. That number is only going to go up. Those people are going to need resources, and they’re going to generate waste. Christopher Kennedy, an engineer who studies “the metabolism of cities” at the University of Toronto, decided to calculate just how much. It wasn’t easy. Megacities tend to incorporate dozens of municipal governments, each with its own way of providing resources to its residents. Twenty-eight researchers in 19 countries helped Kennedy collect the data about what each megacity consumed and produced in a year, and they’ve published their results today in Proceedings of the National Academy of Sciences. Here’s what they came up with:
Cities tend to produce more than their per-capita fair share of economic and social activity, but consume fewer resources than you would expect. When it comes to cities, density equals efficiency. Heating an apartment building that houses 100 people requires less energy than heating 100 separate farmhouses, for example. A subway can transport millions of people per day and requires far less energy than the cars it would take to move an equivalent number of commuters. “Many people, including myself at times, have said cities are going to be the saviors to our global environmental challenges because of these efficiencies,” Kennedy says.
But his data tell a slightly different story. Megacities, he found, produce a staggering 15 percent of the world’s GDP. But they also generate 13 percent of the world’s trash, and use 10 percent of its gasoline. If only about 7 percent of the people live there, that’s disproportionately high. (Water use appears impressively efficient, but remember that megacities generally don’t support agriculture.) What happened to all that urban efficiency? […]